Excretion of oxytetracycline in eggs after medication of laying hens.

The kinetics of oxytetracycline elimination into eggs were determined separately for albumen and yolk after oral administration through either drinking water (0.1-0.25 and 0.5 g/l for 5 days) or feed (300 and 600 ppm for 7 days) or after intramuscular injections (3 X 15 mg/kg body weight and 3 X 30 mg/kg body weight), 24 hours apart. Residues were assayed by a microbiological agar diffusion method, with Bacillus cereus as test-organism. The detection threshold was 0.07 micrograms/g for albumen and 0.2 micrograms/g for yolk. In all cases, the elimination period lasted longer for the yolk; it varied between 0 and 10 days after treatment was discontinued, according to administration routes and dosages. The conditions of oxytetracycline utilization in laying hens are discussed. The oral route only might be used to adhere to the proposals presented by the Joint FAO/WHO Expert Committee on Food Additives.